Detectors for ionizing radiation and, in particular, solid state detectors for ionizing radiation are, e.g., widely used in CT scanners. Such solid state detectors for ionizing radiation comprise, broadly speaking, two main subunits. The first subunit comprises a fluorescent component that is usually referred to as a scintillator or a phosphor which absorbs radiation and in response emits photons in the UV, the visible or the IR region. The second subunit comprises a photodetector which can detect the photons emitted by the scintillator or phosphor and produces corresponding electrical signals.
With regard to the above expressions “scintillator” and “phosphor”, it needs to be noted that both are exchangeable terms and are to be understood within the scope of the invention to refer to solid state luminescent materials that, in response to a stimulation by ionizing radiation such as X-rays, β- or γ-radiation, emit radiation with photons of considerably lower energy.
The expression “ionizing radiation” within the scope of the invention refers to electromagnetic radiation having energy higher than that of ultraviolet radiation.
Detectors for ionizing radiation find broad application in X-ray-based detecting and imaging systems. One of the major medical applications for such detectors and scintillators is in CT scanners.
In particular for their application in CT scanners, it is preferable if those scintillators show a high light yield, so that the CT scanner can be run with as low a radiation dose for the patient as possible. Furthermore, the scintillators used in modern CT scanners should have as low an afterglow as possible, as otherwise the scanning process must be slowed down (e.g. by reducing the rotation frequency) to reduce the influence of the afterglow in subsequent images, affecting the speed of the examination.
Finally, it is also desirable that the scintillators are as transparent as possible to visible light, as otherwise scattering of the photons produced by the interaction between the ionizing radiation and the scintillator occurs, which results in effective background noise during the imaging process, due to optical absorption of the scintillation light in the scintillator.
The two materials that are at the moment commonly used as scintillators for CT scanners are scintillator materials based on Gd2O2S doped with Pr (GOS) and (Y, Gd)2O3 doped with Eu. While those two materials already give reasonable results, it has been shown that GOS, due to the fact that it is not transparent to visible light but merely translucent, shows a reasonably high scattering leading to undesirable effective noise, whereas the (Y, Gd)2O3:Eu based systems show a notable afterglow which could be improved upon for the next generation of CT scanners by replacing this scintillator.